 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.core.commands;

 import java.util.HashMap ;
 import java.util.Map ;
 import java.util.Set ;

 /**
  * <p>
  * An abstract implementation of {@link IObjectWithState}. This provides basic
  * handling for adding and remove state. When state is added, the handler
  * attaches itself as a listener and fire a handleStateChange event to notify
  * this handler. When state is removed, the handler removes itself as a
  * listener.
  * </p>
  * <p>
  * Clients may extend this class.
  * </p>
  *
  * @since 3.2
  */
 public abstract class AbstractHandlerWithState extends AbstractHandler
         implements IObjectWithState, IStateListener {

     /**
      * The map of states currently held by this handler. If this handler has no
      * state (generally, when inactive), then this will be <code>null</code>.
      */
     private Map states = null;

     /**
      * <p>
      * Adds a state to this handler. This will add this handler as a listener to
      * the state, and then fire a handleStateChange so that the handler can
      * respond to the incoming state.
      * </p>
      * <p>
      * Clients may extend this method, but they should call this super method
      * first before doing anything else.
      * </p>
      *
      * @param stateId
      * The identifier indicating the type of state being added; must
      * not be <code>null</code>.
      * @param state
      * The state to add; must not be <code>null</code>.
      */
     public void addState(final String stateId, final State state) {
         if (state == null) {
             throw new NullPointerException ("Cannot add a null state"); //$NON-NLS-1$
 }

         if (states == null) {
             states = new HashMap (3);
         }
         states.put(stateId, state);
         state.addListener(this);
         handleStateChange(state, null);
     }

     public final State getState(final String stateId) {
         if ((states == null) || (states.isEmpty())) {
             return null;
         }

         return (State) states.get(stateId);
     }

     public final String [] getStateIds() {
         if ((states == null) || (states.isEmpty())) {
             return null;
         }

         final Set stateIds = states.keySet();
         return (String []) stateIds.toArray(new String [stateIds.size()]);
     }

     /**
      * <p>
      * Removes a state from this handler. This will remove this handler as a
      * listener to the state. No event is fired to notify the handler of this
      * change.
      * </p>
      * <p>
      * Clients may extend this method, but they should call this super method
      * first before doing anything else.
      * </p>
      *
      * @param stateId
      * The identifier of the state to remove; must not be
      * <code>null</code>.
      */
     public void removeState(final String stateId) {
         if (stateId == null) {
             throw new NullPointerException ("Cannot remove a null state"); //$NON-NLS-1$
 }

         final State state = (State) states.get(stateId);
         if (state != null) {
             state.removeListener(this);
             if (states != null) {
                 states.remove(state);
                 if (states.isEmpty()) {
                     states = null;
                 }
             }
         }
     }
 }

